The present application claims priority under 35 U.S.C. xc2xa7119 to Korean Application No. 30812/2002, filed May 31, 2002, the entire disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates in general to a shadow mask for a color cathode-ray tube and, more particularly, to a shadow mask having improved shock resistance by establishing a ratio of less than 1 between sizes of an electron beam through hole in an axial direction and in a direction vertical to the axial direction when an external shock is impressed on the cathode-ray tube, for example, during a drop intensity test. The electron beam through hole is formed by etching on the shadow mask which is included in the cathode-ray tube.
2. Description of the Background Art
Generally, a cathode-ray tube functions as a principal component in forming an image in an image display device, such as a television picture receiver or a computer monitor.
As shown in FIG. 1, a color cathode-ray tube is sealed by coupling a front glass, depicted as panel 10, to a rear glass, depicted as a funnel 20, thereby resulting in a vacuum within the color cathode-ray tube.
A fluorescent surface 40 of the color cathode-ray tube functions as a luminescent material and is located on an inner side surface of the panel 10. An electron beam 60, which illuminates the fluorescent surface 40, is generated by an electron gun 130. A shadow mask 70 sorts the electron beam 60 generated by the electron gun 130 so that the electron beam 60 can hit a predetermined part of the fluorescent surface 40. A frame 30 fixes and supports the shadow mask 70. A spring 80 and a stud pin 120 couples the frame 30 to the panel 10. An inner shield 90 is coupled to a side surface of the frame 30 opposite to a side surface of the frame 30 facing the panel 10, so that the cathode-ray tube is little affected by outer terrestrial magnetism during operation.
The electron gun 130 is mounted on an inner side surface of a neck portion 140 of the funnel 20. A deflection yoke 50 deflects the electron beam 60 generated by the electron gun 130 to a predetermined direction. A convergence and purity magnet (CPM) 100 controls more precisely the direction of the electron beam 60 deflected by the deflection yoke 50. Both the deflection yoke 50 and the CPM 100 are positioned on an outer side surface of the neck portion 140.
A reinforcing band 110 is mounted on an outer circumferential portion of the color cathode-ray tube that couples the panel 10 to the funnel 20, so that the panel 10 and the funnel 20 do not come apart as a result of atmospheric pressure on or an external disturbance to the color cathode-ray tube.
When the electron beam 60 generated by the electron gun 130 hits the fluorescent surface 40 by a positive voltage applied to the cathode-ray tube, the electron beam 60 is deflected to, for example, upper, lower, left, and right directions by the deflection yoke 50 before the electron beam 60 reaches the florescent surface 40.
The CPM 100 may include magnets of 2, 4, or 6 poles to correct successive tracks of the electron beam 60, so that the electron beam 60 can be more precisely directed on the predetermined fluorescent surface 40 to thereby prevent color purity defects.
The shadow mask 70 is formed in the shape of a dome, and a predetermined gap is maintained between the shadow mask 70 and the inside of the panel 10. As shown in FIG. 2, the shadow mask 70 includes an effective surface portion 71 on which a plurality of electron beam through holes 74 of dot shape are formed. A peripheral portion 72 surrounds the effective surface portion 71 and does not have many electron beam through holes 74. A mask skirt portion 73 is folded vertically from the peripheral portion 72 on the edge part of the peripheral portion 72. The shadow mask 70 has a thickness of about 0.1xcx9c0.3 mm. As shown in FIG. 2, the shadow mask 70, furthermore, has a longer length and a shorter depth.
In the conventional color cathode-ray tube, the electron beam 60 is generated by the electron gun 130, and the electron beam 60 is deflected to the upper, lower, left, and right directions by the deflection yoke 50 before the electron beam 60 reaches the shadow mask 70 and the fluorescent surface 40. Subsequently, the electron beam 60 passes through the shadow mask 70, which sorts the electron beam 60 by a plurality of through holes, and hits the predetermined fluorescent surface 40, thereby forming an image on the fluorescent surface 40.
As shown in FIGS. 3 and 4, the electron beam through hole 74 includes a circular-shaped electron beam incidence hole 74a, formed by etching, facing the inner surface of the funnel 20, and a circular-shaped electron beam exit hole 74b facing the inner surface of the panel 10.
Also, the angle of the electron beam 60 incident on the shadow mask 70 is changed by the specific position on the shadow mask 70 at which the electron beam 60 is incident; therefore, the width of the electron beam exit hole 74b is gradually increased as the beam exit hole 74b approaches the effective surface portion 71 on the shadow mask 70 in order to prevent the electron beam 60 from being scattered.
Although the quality of the color cathode-ray tube can be affected by a number of factors, the color purity of the realized image is the most important factor. The color purity is largely affected by a distortion of the shadow mask 70, which is mainly caused by an external shock. Dropping the color cathode-ray tube, for example, can cause a large shock to the color cathode-ray tube.
Also, when the panel 10, which is relatively heavy compared to other components of the color cathode-ray tube, is dropped to the ground, the shadow mask 70 may suffer severe distortion.
The above distortion is actually caused by the structural characteristics of the shadow mask 70, and this will be described in more detail as follows.
As described above, the shadow mask 70 includes the electron beam through holes 74 of predetermined shape, and the sizes of the electron beam through holes 74 gradually increase as the through holes 74 approach the peripheral parts of the shadow mask 70 in order to prevent the electron beam 60 from being scattered.
As a result, the cross sectional area and volume of the shadow mask 70 gradually decrease near the peripheral parts according to the above changes.
Consequently, in the event that the cathode-ray tube is dropped, the intensity of the shock resulting therefrom on the shadow mask 70 decreases in accordance with the decrease of the cross sectional area on the peripheral parts, and the weight also decreases in accordance with the decrease in volume.
The above structural property causes vibrations in an upper and lower direction on the shadow mask 70, when the side of the color cathode-ray tube on which the panel 10 is formed is dropped.
That is, in the event of an external shock to the cathode-ray tube, the central part of the shadow mask 70, which is exposed to a greater shock and has a greater weight compared to the peripheral parts, has a larger amplitude of vibration than that of the peripheral parts.
Therefore, a greater load impacts the central part of the shadow mask 70; and, accordingly, a distortion is generated having a greater intensity on a boundary of the central part and having a weaker intensity on the peripheral part.
Actually, the shadow mask 70 inside the cathode-ray tube becomes more sensitive as the size of the cathode-ray tube increases. In the event of a shock of a similar intensity, the shadow mask of a larger cathode-ray tube is more likely to suffer permanent damage as a result of a sudden distortion.
In the conventional cathode-ray tube, a length of the electron beam exit hole 74b in a direction facing away from the center of the shadow mask 70 is denoted by Dh, and a length of the electron beam exit hole 74b in a direction perpendicular to the direction facing away from the shadow mask 70 is denoted by Dv. As shown in FIG. 2, the electron beam through hole 74 satisfies the following equation near the peripheral parts of the shadow mask 70:
Dv/Dh≅1.
The diameter of the electron beam through hole 74 on the peripheral parts of the shadow mask 70 is larger than the diameter of the electron beam through hole 74 on the central part of the shadow mask 70 in order to prevent the electron beam 60 passing therethrough from being scattered. Therefore, the electron beam through hole 74 functions as a color-sorting electrode.
However, in the above structure, the structural intensity of the shadow mask is limited by problems caused by the dropping intensity test to which color cathode-ray tubes should, in general, be subjected, and a howling phenomenon may occur.
Therefore, an object of the present invention is to provide a shadow mask for a color cathode-ray tube which is able to improve shock resistance intensity by forming a ratio between sizes of an electron beam through hole in axial direction and in a direction vertically to the axial direction to be less than 1.
To achieve the object of the present invention, as embodied and broadly described herein, there is provided a shadow mask for a color cathode-ray tube including a first portion on which a plurality of electron beam through holes are formed; and a second portion on which no electron beam through holes are formed, the second portion surrounding the first surface portion, wherein each of the plurality of electron beam through holes includes an electron beam exit hole, each of the electron beam exit holes of electron beam through holes formed at a periphery of the first portion near the second portion having a first length Dh in a direction facing away from the center of the shadow mask that is greater than a second length Dv perpendicular to the direction facing away from the center of the shadow mask.
Also, in order to achieve the object of the present invention, there is provided a shadow mask for a color cathode-ray tube including a first portion on which a plurality of electron beam through holes are formed; and a second portion on which no electron beam through holes are formed, the second portion surrounding the first surface portion, wherein each of the plurality of electron beam through holes includes an electron beam exit hole, each of the electron beam exit holes of electron beam through holes formed at a periphery of the first portion near the second portion being formed in an oval shape with a maximum length Dh in a direction facing away from the center of the shadow mask and a minimum length Dv perpendicular to the direction facing away from the center of the shadow mask.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.